Protective Effects of Red Ginseng Against Tacrine-Induced Hepatotoxicity: An Integrated Approach with Network Pharmacology and Experimental Validation.

Introduction: Tacrine, an FDA-approved acetylcholinesterase inhibitor, has shown efficacy in treating Alzheimer's disease, but its clinical use is limited by hepatotoxicity. This study investigates the protective effects of red ginseng against tacrine-induced hepatotoxicity, focusing on oxidative stress. Methods: A network depicting the interaction between compounds and targets was constructed for RG. Effect of RG was determined by MTT and FACS analysis with cells stained by rhodamine 123. Proteins were extracted and subjected to immunoblotting for apoptosis-related proteins. Results: The outcomes of the network analysis revealed a significant association, with 20 out of 82 identified primary RG targets aligning with those involved in oxidative liver damage including notable interactions within the AMPK pathway. in vitro experiments showed that RG, particularly at 1000µg/mL, mitigated tacrine-induced apoptosis and mitochondrial damage, while activating the LKB1-mediated AMPK pathway and Hippo-Yap signaling. In mice, RG also protected the liver injury induced by tacrine, as similar protective effects to silymarin, a well-known drug for liver toxicity protection. Discussion: Our study reveals the potential of RG in mitigating tacrine-induced hepatotoxicity, suggesting the administration of natural products like RG to reduce toxicity in Alzheimer's disease treatment.

In vitro and in vivo Biological Evaluation of Newly Tacrine-Selegiline Hybrids as Multi-Target Inhibitors of Cholinesterases and Monoamine Oxidases for Alzheimer's Disease.

Purpose: Alzheimer's disease (AD) is the most common neurodegenerative disease, and its multifactorial nature increases the difficulty of medical research. To explore an effective treatment for AD, a series of novel tacrine-selegiline hybrids with ChEs and MAOs inhibitory activities were designed and synthesized as multifunctional drugs. Methods: All designed compounds were evaluated in vitro for their inhibition of cholinesterases (AChE/BuChE) and monoamine oxidases (MAO-A/B) along with their blood-brain barrier permeability. Then, further biological activities of the optimizing compound 7d were determined, including molecular model analysis, in vitro cytotoxicity, acute toxicity studies in vivo, and pharmacokinetic and pharmacodynamic property studies in vivo. Results: Most synthesized compounds demonstrated potent inhibitory activity against ChEs/MAOs. Particularly, compound 7d exhibited good and well-balanced activity against ChEs (hAChE: IC50 = 1.57 µM, hBuChE: IC50 = 0.43 µM) and MAOs (hMAO-A: IC50 = 2.30 µM, hMAO-B: IC50 = 4.75 µM). Molecular modeling analysis demonstrated that 7d could interact simultaneously with both the catalytic active site (CAS) and peripheral anionic site (PAS) of AChE in a mixed-type manner and also exhibits binding affinity towards BuChE and MAO-B. Additionally, 7d displayed excellent permeability of the blood-brain barrier, and under the experimental conditions, it elicited low or no toxicity toward PC12 and BV-2 cells. Furthermore, 7d was not acutely toxic in mice at doses up to 2500 mg/kg and could improve the cognitive function of mice with scopolamine-induced memory impairment. Lastly, 7d possessed well pharmacokinetic characteristics. Conclusion: In light of these results, it is clear that 7d could potentially serve as a promising multi-functional drug for the treatment of AD.

Design, synthesis, and biological evaluation of novel donepezil-tacrine hybrids as multi-functional agents with low neurotoxicity against Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory loss and deficits in cognitive domains. Low choline levels, oxidative stress, and neuroinflammation are the primary mechanisms implicated in AD progression. Simultaneous inhibition of acetylcholinesterase (AChE) and reactive oxygen species (ROS) production by a single molecule may provide a new breath of hope for AD treatment. Here, we describe donepezil-tacrine hybrids as inhibitors of AChE and ROS. Four series of derivatives with a ß-amino alcohol linker were designed and synthesized. In this study, the target compounds were evaluated for their ability to inhibit AChE and butyrylcholinesterase (BuChE) in vitro, using tacrine (hAChE, IC50 = 305.78 nM; hBuChE, IC50 = 56.72 nM) and donepezil (hAChE, IC50 = 89.32 nM; hBuChE, IC50 = 9137.16 nM) as positive controls. Compound B19 exhibited an excellent and balanced inhibitory potency against AChE (IC50 = 30.68 nM) and BuChE (IC50 = 124.57 nM). The cytotoxicity assays demonstrated that the PC12 cell viability rates of compound B19 (84.37 %) were close to that of tacrine (87.73 %) and donepezil (79.71 %). Potential therapeutic effects in AD were evaluated using the neuroprotective effect of compounds against H2O2-induced toxicity, and compound B19 (68.77 %) exhibited substantially neuroprotective activity at the concentration of 25 µM, compared with the model group (30.34 %). Furthermore, compound B19 protected PC12 cells from H2O2-induced apoptosis and ROS production. These properties of compound B19 suggested that it was a multi-functional agent with AChE inhibition, anti-oxidative, anti-inflammatory activities, and low toxicity and that it deserves further investigation as a promising agent for AD treatment.

The effects of different acetylcholinesterase inhibitors on EEG patterns in patients with Alzheimer's disease: A systematic review.

OBJECTIVE: Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common type of dementia. The early diagnosis of AD is an important factor for the control of AD progression. Electroencephalography (EEG) can be used for early diagnosis of AD. Acetylcholinesterase inhibitors (AChEIs) are also used for the amelioration of AD symptoms. In this systematic review, we reviewed the effect of different AChEIs including donepezil, rivastigmine, tacrine, physostigmine, and galantamine on EEG patterns in patients with AD. METHODS: PubMed electronic database was searched and 122 articles were found. After removal of unrelated articles, 24 articles were selected for the present study. RESULTS: AChEIs can decrease beta, theta, and delta frequency bands in patients with AD. However, conflicting results were found for alpha band. Some studies have shown increased alpha frequency, while others have shown decreased alpha frequency following treatment with AChEIs. The only difference was the type of drug. CONCLUSIONS: We found that studies reporting the decreased alpha frequency used donepezil and galantamine, while studies reporting the increased alpha frequency used rivastigmine and tacrine. It was suggested that future studies should focus on the effect of different AChEIs on EEG bands, especially alpha frequency in patients with AD, to compare their effects and find the reason for their different influence on EEG patterns. Also, differences between the effects of AChEIs on oligodendrocyte differentiation and myelination may be another important factor. This is the first article investigating the effect of different AChEIs on EEG patterns in patients with AD.

Design, synthesis and biological evaluation of carbamate derivatives incorporating multifunctional carrier scaffolds as pseudo-irreversible cholinesterase inhibitors for the treatment of Alzheimer's disease.

In this study, a series of carbamate derivatives incorporating multifunctional carrier scaffolds were designed, synthesized, and evaluated as potential therapeutic agents for Alzheimer's disease (AD). We used tacrine to modify the aliphatic substituent, and employed rivastigmine, indole and sibiriline fragments as carrier scaffolds. The majority of compounds exhibited good inhibitory activity for cholinesterase. Notably, compound C7 with sibiriline fragment exhibited potent inhibitory activities against human acetylcholinesterase (hAChE, IC50 = 30.35 ± 2.07 nM) and human butyrylcholinesterase (hBuChE, IC50 = 48.03 ± 6.41 nM) with minimal neurotoxicity. Further investigations have demonstrated that C7 exhibited a remarkable capacity to safeguard PC12 cells against H2O2-induced apoptosis and effectively suppressed the production of reactive oxygen species (ROS). Moreover, in an inflammation model of BV2 cells induced by lipopolysaccharide (LPS), C7 effectively attenuated the levels of pro-inflammatory cytokines. After 12 h of dialysis, C7 continued to exhibit an inhibitory effect on cholinesterase activity. An acute toxicity test in vivo demonstrated that C7 exhibited a superior safety profile and no hepatotoxicity compared to the parent nucleus tacrine. In the scopolamine-induced AD mouse model, C7 (20 mg/kg) significantly reduced cholinesterase activity in the brain of the mice. C7 was tested in a pharmacological AD mouse model induced by Aß1-42 and attenuated memory deficits at doses as low as 5 mg/kg. The pseudo-irreversible cholinesterase inhibitory properties and multifunctional therapeutic attributes of C7 render it a promising candidate for further investigation in the treatment of AD.

The Proof-of-Concept of MBA121, a Tacrine-Ferulic Acid Hybrid, for Alzheimer's Disease Therapy.

Great effort has been devoted to the synthesis of novel multi-target directed tacrine derivatives in the search of new treatments for Alzheimer's disease (AD). Herein we describe the proof of concept of MBA121, a compound designed as a tacrine-ferulic acid hybrid, and its potential use in the therapy of AD. MBA121 shows good ß-amyloid (Aß) anti-aggregation properties, selective inhibition of human butyrylcholinesterase, good neuroprotection against toxic insults, such as Aß1-40, Aß1-42, and H2O2, and promising ADMET properties that support translational developments. A passive avoidance task in mice with experimentally induced amnesia was carried out, MBA121 being able to significantly decrease scopolamine-induced learning deficits. In addition, MBA121 reduced the Aß plaque burden in the cerebral cortex and hippocampus in APPswe/PS1ΔE9 transgenic male mice. Our in vivo results relate its bioavailability with the therapeutic response, demonstrating that MBA121 is a promising agent to treat the cognitive decline and neurodegeneration underlying AD.

Sub-pocket-focused designing of tacrine derivatives as potential acetylcholinesterase inhibitors.

Human acetylcholinesterase (hAChE) has a potential role in the management of acetylcholine, one of the neurotransmitters that modulate the overall activity of cholinergic system, AChE inhibitors have a greater impact in the therapeutics. Though the atomic structure of hAChE has been extensively studied, the precise active site geometry upon binding to different ligands are yet to be explored. In the present study, an extensive structural analysis of our recently reported hAChE-tacrine complex has carried out and revealed the presence of two prominent sub-pockets located at the vicinity of the hAChE active site. Structural bioinformatics assisted studies designed 132 putative sub-pockets focused tacrine derivatives (SPFTDs), their molecular docking, free energy estimations revealed that they are stronger than tacrine in terms of binding affinity. Our in vitro studies also supported the in silico findings, all these SPFTDs are having better potencies than tacrine. Cytotoxic nature of these SPFTDs on HepG2 and Neuro-2a cell lines, diminishes the possibilities for future in vivo studies. However, the identification of these sub pockets and the SPFTDs paved a new way to the future drug discovery especially since AChE is one of the promising and approved drug targets in treatment of AD drug discovery.

Polymer drug conjugates containing memantine, tacrine and cinnamic acid: promising nanotherapeutics for the treatment of Alzheimer's disease.

AIM: To prepare polymer-drug conjugates containing a combination of memantine, tacrine, and E)-N-(3-aminopropyl)cinnamide, promising therapeutics for the treatment of neurodegenerative disorders. METHODS: The conjugates were characterised by 1HNMR, particle size analysis, SEM, LC-MS, TEM/EDX, and XRD, followed by in vitro anti-acetylcholinesterase and drug release studies. RESULTS: 1H NMR analysis revealed successful drug conjugation with drug mass percentages in the range of 1.3-6.0% w/w. The drug release from the conjugates was sustained for 10 h in the range of 20-36%. The conjugates' capability to inhibit acetylcholinesterase (AChE) activity was significant with IC50 values in the range of 13-44.4 µm which was more effective than tacrine (IC50 =1698.8 µm). The docking studies further confirmed that the conjugation of the drugs into the polymer improved their anti-acetylcholinesterase activity. CONCLUSION: The drug release profile, particle sizes, and in vitro studies revealed that the conjugates are promising therapeutics for treating neurodegenerative disorders.

Tacrine-Based Hybrids: Past, Present, and Future.

Alzheimer's disease (AD) is a neurodegenerative disorder which is characterized by ß-amyloid (Aß) aggregation, τ-hyperphosphorylation, and loss of cholinergic neurons. The other important hallmarks of AD are oxidative stress, metal dyshomeostasis, inflammation, and cell cycle dysregulation. Multiple therapeutic targets may be proposed for the development of anti-AD drugs, and the "one drug-multiple targets" strategy is of current interest. Tacrine (THA) was the first clinically approved cholinesterase (ChE) inhibitor, which was withdrawn due to high hepatotoxicity. However, its high potency in ChE inhibition, low molecular weight, and simple structure make THA a promising scaffold for developing multi-target agents. In this review, we summarized THA-based hybrids published from 2006 to 2022, thus providing an overview of strategies that have been used in drug design and approaches that have resulted in significant cognitive improvements and reduced hepatotoxicity.

Rosmarinic acid potentiates and detoxifies tacrine in combination for Alzheimer's disease.

BACKGROUND: There is no doubt that Alzheimer's disease (AD) is one of the greatest threats facing mankind today. Within the next few decades, Acetylcholinesterase inhibitors (AChEIs) will be the most widely used treatment for Alzheimer's disease. The withdrawal of the first generation AChEIs drug Tacrine (TAC)/ Cognex from the market as a result of hepatotoxicity has always been an interesting case study. Rosmarinic acid (RA) is a natural compound of phenolic acids that has pharmacological activity for inhibiting Alzheimer's disease, as well as liver protection. PURPOSE AND STUDY DESIGN: In this study, we determined that RA can reduce the hepatotoxicity of TAC, and both of them act synergistically to inhibit the progression of AD in mice. METHODS: In addition to the wild type mice (WT) group, the 6-month-old APP/PS1 (APPswe/PSEN1dE9) double-transgenic (Tg) mice were randomly divided into 6 groups: Tg group, TAC group, RA group, TAC+Silymarin (SIL) group, TAC+RA-L (Rosmarinic Acid Low Dose) goup and TAC+RA-H (Rosmarinic Acid High Dose) group. A series of experiments were carried out, including open field test, Morris water maze test, Hematoxylin - Eosin (HE) staining, Nissl staining, biochemical analysis, immunofluorescence analysis, western blotting analysis and so on. RESULTS: RA combined with TAC could enter the brain tissue of AD mice, and the combination of drugs could better improve the cognitive behavior and brain pathological damage of AD mice, reduce the expression of A ß oligomer, inhibit the deposition of A ß, inhibit the activity of AChE and enhance the level of Ach in hippocampus. Both in vivo and in vitro experiments showed that RA could alleviate the hepatotoxicity or liver injury induced by TAC. The Western blot analysis of the liver of AD mice showed that RA combined with TAC might inhibit the apoptosis of Bcl-2/Bax, reduce the programmed apoptosis mediated by caspase-3 and reduce the burden of liver induced by TAC, could inhibit the development of liver apoptosis by alleviating the hepatotoxicity of TAC and inhibiting the phosphorylation of JNK. CONCLUSION: The potential drug combination that combines rosmarinic acid with tacrine could reduce tacrine's hepatotoxicity as well as enhance its therapeutic effect on Alzheimer's disease.

Recent Modifications of Anti-dementia Agents Focusing on Tacrine and/or Donepezil Analogs.

Alzheimer's Disease (AD) is a multifactorial incurable neurodegenerative disorder. It is characterized by a decline of cholinergic function in parallel with ß-amyloid fibril deposition. Such an imbalance causes severe loss in memory and cognition, leading to behavioral disturbances, depression, and ultimately death. During the last decades, only a few approved drugs were launched onto the market with indications for treating initial and moderate stages of AD. To date, cholinesterase inhibitors (ChEI) are the mainstay line of treatment to ameliorate AD symptoms. Tacrine and Donepezil are the most commonly prescribed anti-dementia drugs, given their potent inhibitory effects. Therefore, many trials have focused on both drugs' structures to synthesize new anti-dementia agents. This paper discusses recent trends of new AD-treating anti-dementia agents focusing on Tacrine and Donepezil analogs and multifunctional hybrid ligands.

Recent Developments in Tacrine-based Hybrids as a Therapeutic Option for Alzheimer's Disease.

Alzheimer's disease (AD) is a multifactorial, irreversible, and age-related neurodegenerative disorder among the elderly. AD attracts attention due to its complex pathogenesis, morbidity and mortality rates, and the limitations of drugs used in the treatment of AD. Cholinesterase inhibitors and N-methyl-D-aspartate (NMDA) receptor antagonists are used in the clinic. While tacrine, donepezil, galantamine, and rivastigmine are cholinesterase inhibitors, memantine is a non-competitive NMDA receptor antagonist. However, these drugs could not delay the progress of AD. The traditional clinical approach which is the one drug-one target concept is not entirely effective in the treatment of AD. Also, it is of high-priority to develop potent and novel anti-AD drugs by the design concept of multitarget directed ligands (MTDLs) which combine pharmacophores interacting with different pathways in AD. This article provides an overview of the noteworthy structural modifications made to tacrine to develop novel candidates for anti-Alzheimer drugs. Due to the complex pathology of AD, multifunctional tacrine-based ligands targeting different hallmarks, ß-amyloid, tau protein, N-methyl-Daspartate receptor, cholinesterases, monoamine oxidases, secretases, have been studied. Here, tacrinebased derivatives including heterocyclic structures such as dihydroxypyridine, chromene, coumarin, pyrazole, triazole, tetrahydroquinolone, dipicolylamine, arylisoxazole were reported with promising anti-AD effects compared to tacrine. In vitro and in vivo assays showed that new tacrine-based hybrids, which are selective, neuroprotective, and non-hepatotoxic, might be considered as remarkable anti-AD drug candidates for further clinical studies.

A Review on Recent Development of Novel Heterocycles as Acetylcholinesterase Inhibitor for the Treatment of Alzheimer's Disease.

Alzheimer's Disease (AD), affecting a large population worldwide, is characterized by the old population's loss of memory and learning ability. Cholinergic deficiency is associated with AD, and various cholinesterase inhibitors have been developed to treat AD, including naturallyderived inhibitors, synthetic analogs, and hybrids. Acetylcholinesterase (AChE) has obtained a renewed interest as a therapeutic target in Alzheimer's disease (AD) due to increased neural cells' function by increasing the concentration of acetylcholine. In this review, we reported the recent development of novel heterocyclic compounds such as coumarin-benzotriazole hybrids, carbazole derivatives, tacrine conjugates, N-benzyl-piperidine-aryl-acyl hydrazones hybrid, spiropyrazoline derivatives, coumarin-dithiocarbamate hybrids, etc., as AChE inhibitors for the treatment of Alzheimer disease. All the bioactive compounds show an effect on different cells and interact simultaneously with the catalytic active site (CAS) and peripheral anionic site (PAS) of AChE with a narrow range of IC50 values from 0.4 nm to 88.21 µm using Ellman's in vitro AChE assay method and show high BBB permeability in vitro. In addition, the in vitro fluorescence assay study using Amplex Red assay kits revealed that all the compounds could inhibit self-induced ß-amyloid (Aß) aggregation with the highest inhibition range from 31.4 to 82%. Furthermore, most of the compounds show a low toxicity profile during in vivo studies. The results suggest that all the compounds constitute promising leads for the AChE targeted approach for Alzheimer's disease.

Privileged multi-target directed propargyl-tacrines combining cholinesterase and monoamine oxidase inhibition activities.

Twenty-four novel compounds bearing tetrahydroacridine and N-propargyl moieties have been designed, synthesised, and evaluated in vitro for their anti-cholinesterase and anti-monoamine oxidase activities. Propargyltacrine 23 (IC50 = 21 nM) was the most potent acetylcholinesterase (AChE) inhibitor, compound 20 (IC50 = 78 nM) showed the best inhibitory human butyrylcholinesterase (hBChE) profile, and ligand 21 afforded equipotent and significant values on both ChEs (human AChE [hAChE]: IC50 = 0.095 ± 0.001 µM; hBChE: IC50 = 0.093 ± 0.003 µM). Regarding MAO inhibition, compounds 7, 15, and 25 demonstrated the highest inhibitory potential towards hMAO-B (IC50 = 163, 40, and 170 nM, respectively). In all, compounds 7, 15, 20, 21, 23, and 25 exhibiting the most balanced pharmacological profile, were submitted to permeability and cell viability tests. As a result, 7-phenoxy-N-(prop-2-yn-1-yl)-1,2,3,4-tetrahydroacridin-9-amine hydrochloride (15) has been identified as a permeable agent that shows a balanced pharmacological profile [IC50 (hAChE) = 1.472 ± 0.024 µM; IC50 (hBChE) = 0.659 ± 0.077 µM; IC50 (hMAO-B) = 40.39 ± 5.98 nM], and consequently, as a new hit-ligand that deserves further investigation, in particular in vivo analyses, as the preliminary cell viability test results reported here suggest that this is a relatively safe therapeutic agent.

Design Synthesis and in vitro Evaluation of Tacrine-flavone Hybrids as Multifunctional Cholinesterase Inhibitors for Alzheimer's Disease.

BACKGROUND: Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder. The multifactorial etiology of AD has led to the design of multitarget directed ligands (MTDL) for AD. Tacrine an acetylcholinesterase (AChE) inhibitor was the first FDA approved drug for AD but is discontinued due to hepatotoxicity. OBJECTIVE: Present research focused on incorporating a flavone to the tacrine nucleus to enhance the anti-Alzheimer's property of the tacrine with the synergistic effect of flavone which is a very good antioxidant. It is expected that the antioxidant property and hepatoprotective nature of flavones will reduce the hepatotoxic side effect of tacrine. METHODS: We designed and synthesized ten flavone substituted tacrine derivatives and evaluated for in vitro AChE and BuChE inhibitoy activity by modified Ellman's method using eeAChE and eqBuChE. In vitro antioxidant activity was studied by DPPH radical scavenging assay. Molecular modeling studies were conducted in Schrodinger and AutoDock Vina with TcAChE(PDB ID:1H23),hAChE(PDB ID:4EY7) and hBuChE(PDB ID:4TPK). RESULTS: All the compounds exhibited potent inhibitory effect on AChE and BuChE with IC50 values in µM concentration. The compounds exhibited very good antioxidant activity in DPPH radical scavenging assay. Among the compounds the compound AF1 showed highest activity with IC50 value of 0.93 µM for AChE and 1.48 µM for BuChE and also showed significant antioxidant activity (2.6 nM). A correlation graph was plotted for IC 50 values vs Dock score and the results are promising with r2 values of 0.62 and 0.73 for AChE and BuChE inhibition respectively which proved the reliability of docking approaches. CONCLUSION: The results highlighted the multifunctional nature of the novel Tacrine-Flavone hybrids and they may be promising MTDL for AD.

Crystal structure of human acetylcholinesterase in complex with tacrine: Implications for drug discovery.

Alzheimer's disease (AD) is one of the most common, progressive neurodegenerative disorders affecting the aged populations. Though various disease pathologies have been suggested for AD, the impairment of the cholinergic system is one of the critical factors for the disease progression. Restoration of the cholinergic transmission through acetylcholinesterase (AChE) inhibitors is a promising disease modifying therapy. Being the first marketed drug for AD, tacrine reversibly inhibits AChE and thereby slows the breakdown of the chemical messenger acetylcholine (ACh) in the brain. However, the atomic level of interactions of tacrine towards human AChE (hAChE) is unknown for years. Hence, in the current study, we report the X-ray structure of hAChE-tacrine complex at 2.85 Å resolution. The conformational heterogeneity of tacrine within the electron density was addressed with the help of molecular mechanics assisted methods and the low-energy ligand configuration is reported, which provides a mechanistic explanation for the high binding affinity of tacrine towards AChE. Additionally, structural comparison of reported hAChE structures sheds light on the conformational selection and induced fit effects of various active site residues upon binding to different ligands and provides insight for future drug design campaigns against AD where AChE is a drug target.

Novel tacrine-based acetylcholinesterase inhibitors as potential agents for the treatment of Alzheimer's disease: Quinolotacrine hybrids.

A new series of quinolotacrine hybrids including cyclopenta- and cyclohexa-quinolotacrine derivatives were designed, synthesized, and assessed as anti-cholinesterase (ChE) agents. The designed derivatives indicated higher inhibitory effect on the acetylcholinesterase (AChE) with IC50 values of 0.285-100 µM compared to butyrylcholinesterase (BChE) with IC50 values of > 100 µM. Of these compounds, cyclohexa-quinolotacrine hybrids displayed a little better anti-AChE activity than cyclopenta-quinolotacrine hybrids. Compound 8-amino-7-(3-hydroxyphenyl)-5,7,9,10,11,12-hexahydro-6H-pyrano[2,3-b:5,6-c'] diquinolin-6-one (6m) including 3-hydroxyphenyl and cyclohexane ring moieties exhibited the best AChE inhibitory activity with IC50 value of 0.285 µM. The kinetic and molecular docking studies indicated that compound 6m occupied both the catalytic anionic site (CAS) and peripheral anionic site (PAS) of AChE as a mixed inhibitor. Using neuroprotective assay against H2O2-induced cell death in PC12 cells, the compound 6h illustrated significant protection among the assessed compounds. In silico ADME studies estimated good drug-likeness for the designed compounds. As a result, these quinolotacrine hybrids can be very encouraging AChE inhibitors to treat Alzheimer's disease. A novel series of quinolotacrine hybrids were designed, synthesized, and evaluated against AChE and BChE enzymes as potential agents for the treatment of AD. The hybrids showed good to significant inhibitory activity against AChE (0.285-100 µM) compared to butyrylcholinesterase (BChE) with IC50 values of > 100 µM. Among them, compound 8-amino-7-(3-hydroxyphenyl)-5,7,9,10,11,12-hexahydro-6H-pyrano[2,3-b:5,6-c'] diquinolin-6-one (6 m) bearing 3-hydroxyphenyl moiety and cyclohexane ring exhibited the highest anti-AChE activity with IC50 value of 0.285 µM. The kinetic and molecular docking studies illustrated that compound 6 m is a mixed inhibitor and binds to both the catalytic anionic site (CAS) and peripheral anionic site (PAS) of AChE.

Multi-Target Drug Design of Anti-Alzheimer's Disease based on Tacrine.

Alzheimer's disease (AD) is a progressive neurodegenerative disease with concealed onset, which is characterized by the damage of the cholinergic system, deposition, and accumulation of ß- amyloid protein (Aß) and neurofibrillary tangles. Because the cholinergic system plays a key role in the process of brain memory, it has become one of the important targets in anti-AD research. In view of the complicated pathological characteristics of AD, the multi-target directed ligands (MTDLs) that can act on multiple targets are considered to be an effective treatment strategy at present. Tacrine, as the first acetylcholinesterase (AChE) inhibitor, has been discontinued because of its hepatotoxicity, but its core structure is simple and easy to modify. By using tacrine to target the active catalytic site (CAS), the tacrine-based MTDLs can act on both CAS and peripheral anion site (PAS) of AChE to serve as a dual-site AChE inhibitor. Additionally, the tacrine-based MTDLs can also be designed on the basis of other theories of AD, for example, introducing functional moieties to modulate the formation of ß-amyloid (Aß), oxidation resistance, or metal chelation. In this paper, the research progress of tacrine-based MTDLs is summarized.

Conjugation of tacrine with genipin derivative not only enhances effects on AChE but also leads to autophagy against Alzheimer's disease.

Seven tacrine/CHR21 conjugates have been designed and synthesized. Compound 8-7 was confirmed as the most active AChE inhibitor with IC50 value of 5.8 ± 1.4 nM, which was 7.72-fold stronger than tacrine. It was also shown as a strong BuChE inhibitor (IC50 value of 3.7 ± 1.3 nM). 8-7 was clearly highlighted not only as an excellent ChEs inhibitor, but also as a good modulator on protein expression of AChE, p53, Bax, Bcl-2, LC3, p62, and ULK, indicating its functions against programmed cell apoptosis and decrease of autophagy. 8-7 significantly reversed the glutamate-induced dysfunctions including excessive calcium influx and release from internal organelles, overproduction of nitric oxide (NO) and Aß high molecular weight oligomer. This compound can penetrate blood-brain barrier (BBB). The in vivo hepatotoxicity assay indicated that 8-7 was much less toxic than tacrine. Altogether, these data strongly support that 8-7 is a potential multitarget-directed ligand (MTDL) for treating Alzheimer's disease (AD).

Tacrine accelerates spatial long-term memory via improving impaired neural oscillations and modulating GAD isomers including neuro-receptors in the hippocampus of APP/PS1 AD mice.

Tacrine (Amino tetrahydroacridine hydrochloride hydrate) is a non-competitive and reversible inhibitor of acetylcholine esterase, and butylcholinesterase. Alzheimer's disease (AD) shows multiple types of pathological pathway in which cholinergic neuron deficiency is 95 % popular and the oldest pathological mechanism. However, the effect of tacrine on the hippocampal dependent memory is not yet known. In this study, we did verify that tacrine induced recovery of the specific pattern associated memory along with long-term memory through the improvement in the pattern of neural oscillation from deficits condition in the hippocampus of 6th month old AD mice. Our results showed that tacrine improved the performance of Morris water maze related spatial cognitive functions, and enhanced LTP in AD-TAC mice. Furthermore, our results implied that tacrine strongly improve the patterns of neural oscillations, and hippocampal synaptic plasticity in the 6th month old APP-PS1 double transgenic AD-TAC mice via changing the theta and alpha power spectra including with the improvement in theta, alpha and gamma synchronization. Moreover, tacrine generated the improvement in the theta cross spectra, theta-gamma phase-phase synchronization and theta-gamma phase-amplitude coupling. Besides, the data represented that tacrine accelerated the expression of NR2B, SYP and GAD65 while it caused deceleration on the expression of GAD67 neurotransmitter and Aß. Thus, our results infer that tacrine works as a strong causative agent for improving the specific pattern-associated spatial long-term memory in the AD mice without showing any side effect.